Typical electrophotographic (EP) devices have a spinning polygon mirror that directs a laser beam on a photoconductor, such as a drum, to create one or more scan lines of a latent to-be-printed image. With reference to FIG. 1, multiple scan lines (1-6) are shown and all extend in the direction of the arrows left-to-right in the scanning direction 10. Conveniently, common referencing of all scan lines can occur relative to a single laser beam sensor position 12, known commonly as a horizontal synchronization (or “hsync”) position. Often, the hsync signal is defined in units of time for the engine of the EP device and its apparent location exists in a space somewhere off the edge of the printed page.
However, it has recently been suggested that torsion oscillator or resonant galvanometer structures can replace the traditional spinning polygon mirror. In this manner, scan lines occur in both the forward and backward directions (e.g., bi-directionally) thereby increasing efficiency of the EP device. Because of their small size, and fabrication techniques, the structures are also fairly suggested to reduce the relative cost of manufacturing. Unfortunately, scanning in two directions adds complexity to image referencing since two reference points need occur at opposite ends of the printed page and even the slightest of deviations between scan lines amplifies print image imperfections. Also, EP device parameters, such as beam sensor signal delays, optical component alignment, and galvanometer or oscillator scan profile nonlinearity must be measured and accounted for.
Accordingly, there exists a need in the art for calibration techniques for bi-directionally scanning EP devices. Particularly, there are needs by which the print alignment is accounted for at one or more of the stages of manufacturing, servicing or end-user operation. Naturally, any improvements should further contemplate good engineering practices, such as relative inexpensiveness, stability, low complexity, ease of implementation, etc.